Earlier, whole-rock data assisted in constraining magmatic processes accountable for the evolution of Giant Plagioclase Basalt (GPB), although plagioclase chemistry data-based implications are rare and critical, while combining with bulk-rock chemistry to understand magmatic processes regionally. For this reason, giant and small-size plagioclase grains were analyzed using Electron Probe Microanalysis (EPMA). Core to margin of the Kalsubai Subgroup GPB grains show significant variation ranging from An$_{99}$Ab$_1$–An$_{94}$Ab$_6$ to An$_{65}$Ab$_{35}$–An$_5$Ab$_{95}$, respectively. Nucleation of An-rich core initiated in the midlithospheric level at elevated temperatures, varying between 1490 and 1510°C, but successive An-poor intermediate and marginal layers crystallized at low temperatures between 1200–1360°C and 910–930°C that also in shallower depth, respectively. Moreover, supercharged feldspar-rich magma persisted throughout the Kalsubai Subgroup lavas, as noticed by the absence of zoned plagioclase. Almost similar processes were followed, but in a subdued manner at 1220–1300°C temperature in the Kevlari–Kalan area that lies ${\sim}$900 km apart in the eastern Deccan Volcanic Province (DVP). Presence of plume-fed magma chamber is also justified by the size and thickness of the Kalsubai Subgroup lavas. Uninterrupted recharge of magma source was continued as Ab/An value remains constant throughout the Kalsubai Subgroup lava sequence. Further, residence period of 3.2–17.4 ka is assigned to GPB of the Kalsubai Subgroup. Owing to high eruption rate, younger formations of the main DVP do not contain GPB, but Kevlari Kalan GPB contains labradorite (An$_{60}$Ab$_{40}$–An$_{50}$Ab$_{50}$) rich plagioclase, crystallized during storage of the magma for a shorter interval comparing to Kalsubai Subgroup GPB lavas.

$\bf{Highlights}$

$\bullet$ Giant plagioclase contains Ca- rich (An99) core and Ca-poor (An65) rim

$\bullet$ Three crystallization episodes assigned to Kalsubai GPB and one to Kevlari Kalan GPB

$\bullet$ Owing to high eruption rate, younger western DVP is devoid of GPB.